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  2. JavaScript
  3. JavaScript 参考
  4. 语句和声明

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JavaScript applications consist of statements with an appropriate syntax. A single statement may span multiple lines. Multiple statements may occur on a single line if each statement is separated by a semicolon. This isn't a keyword, but a group of keywords.

语句和声明 (按类别)

对于按字母顺序清单，请参阅左侧边栏。

控制流

Block

A block statement is used to group zero or more statements. The block is delimited by a pair of curly brackets.

break

Terminates the current loop, switch, or label statement and transfers program control to the statement following the terminated statement.

continue

Terminates execution of the statements in the current iteration of the current or labeled loop, and continues execution of the loop with the next iteration.

Empty

An empty statement is used to provide no statement, although the JavaScript syntax would expect one.

if...else

Executes a statement if a specified condition is true. If the condition is false, another statement can be executed.

switch

Evaluates an expression, matching the expression's value to a case clause, and executes statements associated with that case.

throw

抛出用户定义的异常。

try...catch

Marks a block of statements to try, and specifies a response, should an exception be thrown.

声明

var

声明变量，可选初始化其值。

let

声明块作用域局部变量，可选初始化其值。

const

声明只读命名常量。

函数和类

function

采用指定参数声明函数。

function*
生成器函数启用写入 iterators 更容易。
async function

采用指定参数声明异步函数。

return

指定由函数返回的值。

class

声明类。

迭代

do...while

Creates a loop that executes a specified statement until the test condition evaluates to false. The condition is evaluated after executing the statement, resulting in the specified statement executing at least once.

for

Creates a loop that consists of three optional expressions, enclosed in parentheses and separated by semicolons, followed by a statement executed in the loop.

for each...in

Iterates a specified variable over all values of object's properties. For each distinct property, a specified statement is executed.

for...in

Iterates over the enumerable properties of an object, in arbitrary order. For each distinct property, statements can be executed.

for...of
Iterates over iterable objects (including arrays ，像数组对象， 迭代器和生成器 ), invoking a custom iteration hook with statements to be executed for the value of each distinct property.
for await...of
Iterates over async iterable objects, array-like objects, 迭代器和生成器 , invoking a custom iteration hook with statements to be executed for the value of each distinct property.
while

Creates a loop that executes a specified statement as long as the test condition evaluates to true. The condition is evaluated before executing the statement.

其它

debugger

Invokes any available debugging functionality. If no debugging functionality is available, this statement has no effect.

export

Used to export functions to make them available for imports in external modules, and other scripts.

import

Used to import functions exported from an external module, another script.

import.meta

An object exposing context-specific metadata to a JavaScript module.

label
Provides a statement with an identifier that you can refer to using a break or continue 语句。
with

扩展语句的作用域链。

规范

规范
ECMAScript (ECMA-262)
The definition of 'ECMAScript Language: Statements and Declarations' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据
Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet Node.js
async function Chrome 55 Edge 15 Firefox 52 IE No Opera 42 Safari 10.1 WebView Android 55 Chrome Android 55 Firefox Android 52 Opera Android 42 Safari iOS 10.3 Samsung Internet Android 6.0 nodejs 7.6.0
7.6.0
7.0.0 Disabled
Disabled From version 7.0.0: this feature is behind the --harmony runtime flag.
block Chrome 1 Edge 12 Firefox 1 IE 11 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
break Chrome 1 Edge 12 Firefox 1 IE 3 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
class Chrome 49
49
不支持 42 — 49
Strict mode is required.
不支持 42 — 49 Disabled
Disabled ). To change preferences in Chrome, visit
Edge 13 Firefox 45 IE No Opera 36
36
不支持 29 — 36
Strict mode is required.
不支持 29 — 36 Disabled
Disabled From version 29 until version 36 (exclusive): this feature is behind the Experimental JavaScript preference (needs to be set to Enabled ).
Safari 10.1 WebView Android 49
49
不支持 42 — 49
Strict mode is required.
Chrome Android 49
49
不支持 42 — 49
Strict mode is required.
不支持 42 — 49 Disabled
Disabled ). To change preferences in Chrome, visit
Firefox Android 45 Opera Android 36
36
不支持 29 — 36
Strict mode is required.
不支持 29 — 36 Disabled
Disabled From version 29 until version 36 (exclusive): this feature is behind the Experimental JavaScript preference (needs to be set to Enabled ).
Safari iOS 10.3 Samsung Internet Android 5.0
5.0
不支持 4.0 — 5.0
Strict mode is required.
nodejs 6.0.0
const Chrome 21 Edge 12 Firefox 36
36
Prior to Firefox 13, const is implemented, but re-assignment is not failing.
Prior to Firefox 46, a TypeError was thrown on redeclaration instead of a SyntaxError .
IE 11 Opera 9 Safari 5.1 WebView Android ≤37 Chrome Android 25 Firefox Android 36
36
Prior to Firefox 13, const is implemented, but re-assignment is not failing.
Prior to Firefox 46, a TypeError was thrown on redeclaration instead of a SyntaxError .
Opera Android 10.1 Safari iOS 6 Samsung Internet Android 1.5 nodejs 6.0.0
continue Chrome 1 Edge 12 Firefox 1 IE 3 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
debugger Chrome 5 Edge 12 Firefox 1 IE 4 Opera 10 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 4.2 Samsung Internet Android 1.0 nodejs 0.1.100
do...while Chrome 1 Edge 12 Firefox 1 IE 4 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
Empty statement ( ; ) Chrome 3 Edge 12 Firefox 1 IE 3 Opera 3 Safari 5 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 4.2 Samsung Internet Android 1.0 nodejs 0.1.100
export Chrome 61 Edge 16
16
15 Disabled
Disabled From version 15: this feature is behind the Experimental JavaScript Features preference.
Firefox 60
60
不支持 54 — 60 Disabled
Disabled From version 54 until version 60 (exclusive): this feature is behind the dom.moduleScripts.enabled preference. To change preferences in Firefox, visit about:config.
IE No Opera 48 Safari 10.1 WebView Android No Chrome Android 61 Firefox Android 60
60
不支持 54 — 60 Disabled
Disabled From version 54 until version 60 (exclusive): this feature is behind the dom.moduleScripts.enabled preference. To change preferences in Firefox, visit about:config.
Opera Android 45 Safari iOS 10.3 Samsung Internet Android 8.0 nodejs 13.2.0
13.2.0
Modules must either have a filename ending in .mjs , or the nearest parent package.json file must contain "type": "module" . See Node's ECMAScript Modules documentation 了解更多细节。
12.0.0 Disabled
Modules must either have a filename ending in .mjs , or the nearest parent package.json file must contain "type": "module" . See Node's ECMAScript Modules documentation 了解更多细节。
Disabled From version 12.0.0: this feature is behind the --experimental-modules runtime flag.
8.5.0 Disabled
Module filenames must end with .mjs , not .js. See Node's ECMAScript Modules documentation 了解更多细节。
Disabled From version 8.5.0: this feature is behind the --experimental-modules runtime flag.
for Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
for await...of Chrome 63 Edge 79 Firefox 57 IE No Opera 50 Safari 11 WebView Android 63 Chrome Android 63 Firefox Android 57 Opera Android 46 Safari iOS 11 Samsung Internet Android 8.0 nodejs 10.0.0
10.0.0
不支持 8.10.0 — 10.0.0 Disabled
Disabled From version 8.10.0 until version 10.0.0 (exclusive): this feature is behind the --harmony-async-iteration runtime flag.
for...in Chrome 1 Edge 12 Firefox 1 IE 6 Opera 2 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
for...of Chrome 38 Edge 12 Firefox 13
13
Prior to Firefox 51, using the for...of loop construct with the const keyword threw a SyntaxError ("missing = in const declaration").
IE No Opera 25 Safari 7 WebView Android 38 Chrome Android 38 Firefox Android 14
14
Prior to Firefox 51, using the for...of loop construct with the const keyword threw a SyntaxError ("missing = in const declaration").
Opera Android 25 Safari iOS 7 Samsung Internet Android 3.0 nodejs 0.12
function Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
function* Chrome 39 Edge 13 Firefox 26 IE No Opera 26 Safari 10 WebView Android 39 Chrome Android 39 Firefox Android 26 Opera Android 26 Safari iOS 10 Samsung Internet Android 4.0 nodejs 4.0.0
4.0.0
0.12 Disabled
Disabled From version 0.12: this feature is behind the --harmony runtime flag.
if...else Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
import Chrome 61 Edge 16
16
15 Disabled
Disabled From version 15: this feature is behind the Experimental JavaScript Features preference.
Firefox 60
60
不支持 54 — 60 Disabled
Disabled From version 54 until version 60 (exclusive): this feature is behind the dom.moduleScripts.enabled preference. To change preferences in Firefox, visit about:config.
IE No Opera 48 Safari 10.1 WebView Android 61 Chrome Android 61 Firefox Android 60
60
不支持 54 — 60 Disabled
Disabled From version 54 until version 60 (exclusive): this feature is behind the dom.moduleScripts.enabled preference. To change preferences in Firefox, visit about:config.
Opera Android 45 Safari iOS 10.3 Samsung Internet Android 8.0 nodejs 13.2.0
13.2.0
Modules must either have a filename ending in .mjs , or the nearest parent package.json file must contain "type": "module" . See Node's ECMAScript Modules documentation 了解更多细节。
12.0.0 Disabled
Modules must either have a filename ending in .mjs , or the nearest parent package.json file must contain "type": "module" . See Node's ECMAScript Modules documentation 了解更多细节。
Disabled From version 12.0.0: this feature is behind the --experimental-modules runtime flag.
8.5.0 Disabled
Module filenames must end with .mjs , not .js. See Node's ECMAScript Modules documentation 了解更多细节。
Disabled From version 8.5.0: this feature is behind the --experimental-modules runtime flag.
import.meta Chrome 64 Edge 79 Firefox 62 IE No Opera 51 Safari 11.1 WebView Android 64 Chrome Android 64 Firefox Android 62 Opera Android 47 Safari iOS 12 Samsung Internet Android 9.0 nodejs 10.4.0
label Chrome 1 Edge 12 Firefox 1 IE 4 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
let Chrome 49
49
不支持 48 — 49 Disabled
Support outside of 严格模式 .
Disabled From version 48 until version 49 (exclusive): this feature is behind the Enable Experimental JavaScript Features preference. To change preferences in Chrome, visit chrome://flags.
不支持 41 — 49
严格模式 is required.
Edge 14
14
不支持 12 — 14
In Edge 12 and 13, let within a for loop initializer does not create a separate variable for each loop iteration as defined by ES2015. Instead, it behaves as though the loop were wrapped in a scoping block with the let immediately before the loop.
Firefox 44
44
Prior to Firefox 44, let is only available to code blocks in HTML wrapped in a <script type="application/javascript;version=1.7"> block (or higher version) and has different semantics (e.g. no temporal dead zone).
Prior to Firefox 46, a TypeError is thrown on redeclaration instead of a SyntaxError .
Firefox 54 adds support of let in workers.
IE 部分支持 11
部分支持 11
在 Internet Explorer， let within a for loop initializer does not create a separate variable for each loop iteration as defined by ES2015. Instead, it behaves as though the loop were wrapped in a scoping block with the let immediately before the loop.
Opera 17 Safari 10 WebView Android 49
49
不支持 41 — 49
严格模式 is required.
Chrome Android 49
49
不支持 48 — 49 Disabled
Support outside of 严格模式 .
Disabled From version 48 until version 49 (exclusive): this feature is behind the Enable Experimental JavaScript Features preference. To change preferences in Chrome, visit chrome://flags.
不支持 41 — 49
严格模式 is required.
Firefox Android 44
44
Prior to Firefox 44, let is only available to code blocks in HTML wrapped in a <script type="application/javascript;version=1.7"> block (or higher version) and has different semantics (e.g. no temporal dead zone).
Prior to Firefox 46, a TypeError is thrown on redeclaration instead of a SyntaxError .
Firefox 54 adds support of let in workers.
Opera Android 18 Safari iOS 10 Samsung Internet Android 5.0
5.0
不支持 4.0 — 5.0
严格模式 is required.
nodejs 6.0.0
return Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
switch Chrome 1 Edge 12 Firefox 1 IE 4 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
throw Chrome 1 Edge 12 Firefox 1 IE 5 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
try...catch Chrome 1 Edge 12 Firefox 1 IE 5 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
var Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
while Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
with 弃用 Chrome 1 Edge 12 Firefox 1 IE 3 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100

图例

完整支持

完整支持

部分支持

部分支持

不支持

不支持

弃用。不要用于新网站。

弃用。不要用于新网站。

见实现注意事项。

用户必须明确启用此特征。

用户必须明确启用此特征。

另请参阅

元数据

  • 最后修改：
  1. JavaScript
  2. 教程：
  3. 完全初学者
    1. JavaScript 基础
    2. JavaScript 第一步
    3. JavaScript 构建块
    4. 引入 JavaScript 对象
  4. JavaScript 指南
    1. 介绍
    2. 语法和类型
    3. 控制流程和错误处理
    4. 循环和迭代
    5. 函数
    6. 表达式和运算符
    7. 数字和日期
    8. 文本格式化
    9. 正则表达式
    10. 索引集合
    11. 键控集合
    12. Working with objects
    13. 对象模型的细节
    14. Using promises
    15. 迭代器和生成器
    16. Meta programming
    17. JavaScript 模块
  5. 中间体
    1. Client-side JavaScript frameworks
    2. 客户端侧 Web API
    3. 重新介绍 JavaScript
    4. JavaScript 数据结构
    5. 相等比较和相同
    6. 闭包
  6. 高级
    1. 继承和原型链
    2. 严格模式
    3. JavaScript 类型数组
    4. 内存管理
    5. 并发模型和事件循环
  7. 参考：
  8. 内置对象
    1. AggregateError
    2. Array
    3. ArrayBuffer
    4. AsyncFunction
    5. Atomics
    6. BigInt
    7. BigInt64Array
    8. BigUint64Array
    9. 布尔
    10. DataView
    11. Date
    12. Error
    13. EvalError
    14. FinalizationRegistry
    15. Float32Array
    16. Float64Array
    17. Function
    18. Generator
    19. GeneratorFunction
    20. Infinity
    21. Int16Array
    22. Int32Array
    23. Int8Array
    24. InternalError
    25. Intl
    26. JSON
    27. Map
    28. Math
    29. NaN
    30. Number
    31. Object
    32. Promise
    33. Proxy
    34. RangeError
    35. ReferenceError
    36. Reflect
    37. RegExp
    38. Set
    39. SharedArrayBuffer
    40. String
    41. Symbol
    42. SyntaxError
    43. TypeError
    44. TypedArray
    45. URIError
    46. Uint16Array
    47. Uint32Array
    48. Uint8Array
    49. Uint8ClampedArray
    50. WeakMap
    51. WeakRef
    52. WeakSet
    53. WebAssembly
    54. decodeURI()
    55. decodeURIComponent()
    56. encodeURI()
    57. encodeURIComponent()
    58. escape()
    59. eval()
    60. globalThis
    61. isFinite()
    62. isNaN()
    63. null
    64. parseFloat()
    65. parseInt()
    66. undefined
    67. unescape()
    68. uneval()
  9. 表达式 & 运算符
    1. Addition (+)
    2. Addition assignment (+=)
    3. Assignment (=)
    4. Bitwise AND (&)
    5. Bitwise AND assignment (&=)
    6. Bitwise NOT (~)
    7. Bitwise OR (|)
    8. Bitwise OR assignment (|=)
    9. Bitwise XOR (^)
    10. Bitwise XOR assignment (^=)
    11. Comma operator (,)
    12. 条件 (三元) 运算符
    13. Decrement (--)
    14. Destructuring assignment
    15. Division (/)
    16. Division assignment (/=)
    17. Equality (==)
    18. Exponentiation (**)
    19. Exponentiation assignment (**=)
    20. 函数表达式
    21. Greater than (>)
    22. Greater than or equal (>=)
    23. Grouping operator ( )
    24. Increment (++)
    25. Inequality (!=)
    26. Left shift (<<)
    27. Left shift assignment (<<=)
    28. Less than (<)
    29. Less than or equal (<=)
    30. Logical AND (&&)
    31. Logical AND assignment (&&=)
    32. Logical NOT (!)
    33. Logical OR (||)
    34. Logical OR assignment (||=)
    35. Logical nullish assignment (??=)
    36. Multiplication (*)
    37. Multiplication assignment (*=)
    38. Nullish coalescing operator (??)
    39. 对象初始化器
    40. 运算符优先级
    41. Optional chaining (?.)
    42. Pipeline operator (|>)
    43. 特性访问器
    44. Remainder (%)
    45. Remainder assignment (%=)
    46. Right shift (>>)
    47. Right shift assignment (>>=)
    48. Spread syntax (...)
    49. Strict equality (===)
    50. Strict inequality (!==)
    51. Subtraction (-)
    52. Subtraction assignment (-=)
    53. Unary negation (-)
    54. Unary plus (+)
    55. Unsigned right shift (>>>)
    56. Unsigned right shift assignment (>>>=)
    57. 异步函数表达式
    58. await
    59. class expression
    60. delete operator
    61. function* 表达式
    62. in operator
    63. instanceof
    64. new operator
    65. new.target
    66. super
    67. this
    68. typeof
    69. void 运算符
    70. yield
    71. yield*
  10. 语句 & 声明
    1. async function
    2. block
    3. break
    4. class
    5. const
    6. continue
    7. debugger
    8. do...while
    9. empty
    10. export
    11. for
    12. for await...of
    13. for...in
    14. for...of
    15. 函数声明
    16. function*
    17. if...else
    18. import
    19. import.meta
    20. label
    21. let
    22. return
    23. switch
    24. throw
    25. try...catch
    26. var
    27. while
    28. with
  11. 函数
    1. 箭头函数表达式
    2. 默认参数
    3. 方法定义
    4. 其余参数
    5. 自变量对象
    6. getter
    7. setter
  12. 类
    1. Private class fields
    2. Public class fields
    3. 构造函数
    4. extends
    5. static
  13. 错误
    1. Error: Permission denied to access property "x"
    2. InternalError: too much recursion
    3. RangeError: argument is not a valid code point
    4. RangeError: invalid array length
    5. RangeError: invalid date
    6. RangeError: precision is out of range
    7. RangeError: radix must be an integer
    8. RangeError: repeat count must be less than infinity
    9. RangeError: repeat count must be non-negative
    10. ReferenceError: "x" is not defined
    11. ReferenceError: assignment to undeclared variable "x"
    12. ReferenceError: can't access lexical declaration`X' before initialization
    13. ReferenceError: deprecated caller or arguments usage
    14. ReferenceError: invalid assignment left-hand side
    15. ReferenceError: reference to undefined property "x"
    16. SyntaxError: "0"-prefixed octal literals and octal escape seq. are deprecated
    17. SyntaxError: "use strict" not allowed in function with non-simple parameters
    18. SyntaxError: "x" is a reserved identifier
    19. SyntaxError: JSON.parse: bad parsing
    20. SyntaxError: Malformed formal parameter
    21. SyntaxError: Unexpected token
    22. SyntaxError: Using //@ to indicate sourceURL pragmas is deprecated. Use //# instead
    23. SyntaxError: a declaration in the head of a for-of loop can't have an initializer
    24. SyntaxError: applying the 'delete' operator to an unqualified name is deprecated
    25. SyntaxError: for-in loop head declarations may not have initializers
    26. SyntaxError: function statement requires a name
    27. SyntaxError: identifier starts immediately after numeric literal
    28. SyntaxError: illegal character
    29. SyntaxError: invalid regular expression flag "x"
    30. SyntaxError: missing ) after argument list
    31. SyntaxError: missing ) after condition
    32. SyntaxError: missing : after property id
    33. SyntaxError: missing ; before statement
    34. SyntaxError: missing = in const declaration
    35. SyntaxError: missing ] after element list
    36. SyntaxError: missing formal parameter
    37. SyntaxError: missing name after . operator
    38. SyntaxError: missing variable name
    39. SyntaxError: missing } after function body
    40. SyntaxError: missing } after property list
    41. SyntaxError: redeclaration of formal parameter "x"
    42. SyntaxError: return not in function
    43. SyntaxError: test for equality (==) mistyped as assignment (=)?
    44. SyntaxError: unterminated string literal
    45. TypeError: "x" has no properties
    46. TypeError: "x" is (not) "y"
    47. TypeError: "x" is not a constructor
    48. TypeError: "x" is not a function
    49. TypeError: "x" is not a non-null object
    50. TypeError: "x" is read-only
    51. TypeError: 'x' is not iterable
    52. TypeError: More arguments needed
    53. TypeError: Reduce of empty array with no initial value
    54. TypeError: X.prototype.y called on incompatible type
    55. TypeError: can't access dead object
    56. TypeError: can't access property "x" of "y"
    57. TypeError: can't assign to property "x" on "y": not an object
    58. TypeError: can't define property "x": "obj" is not extensible
    59. TypeError: can't delete non-configurable array element
    60. TypeError: can't redefine non-configurable property "x"
    61. TypeError: cannot use 'in' operator to search for 'x' in 'y'
    62. TypeError: cyclic object value
    63. TypeError: invalid 'instanceof' operand 'x'
    64. TypeError: invalid Array.prototype.sort argument
    65. TypeError: invalid arguments
    66. TypeError: invalid assignment to const "x"
    67. TypeError: property "x" is non-configurable and can't be deleted
    68. TypeError: setting getter-only property "x"
    69. TypeError: variable "x" redeclares argument
    70. URIError: malformed URI sequence
    71. Warning: -file- is being assigned a //# sourceMappingURL, but already has one
    72. Warning: 08/09 is not a legal ECMA-262 octal constant
    73. Warning: Date.prototype.toLocaleFormat is deprecated
    74. Warning: JavaScript 1.6's for-each-in loops are deprecated
    75. Warning: String.x is deprecated; use String.prototype.x instead
    76. Warning: expression closures are deprecated
    77. Warning: unreachable code after return statement
  14. 杂项
    1. JavaScript 技术概述
    2. 词法语法
    3. JavaScript 数据结构
    4. Enumerability and ownership of properties
    5. Iteration protocols
    6. 严格模式
    7. 过渡到严格模式
    8. 模板文字
    9. 弃用特征

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